Brake caliper

ABSTRACT

A brake caliper has a brake pad having a backplate with a friction material attached to one side and a loading face on an opposite side. The caliper further includes a piston that applies a force to the loading face. The brake pad is releasably attached to the piston, thereby eliminating a separate brake pad retaining structure in the caliper.

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to United Kingdom (GB) patent application No. 0218165.9 filed on Aug. 6, 2002.

TECHNICAL FIELD

[0002] The present invention relates to brake pad backplates, brake pads and brake calipers.

BACKGROUND OF THE INVENTION

[0003] Brake calipers, which are known in the art, force brake pads towards a brake disc to effect braking of the disc. The brake pads comprise a brake pad backplate, typically stamped from sheet steel, onto which is fixed friction material. The friction material is forced into engagement with the brake disc to effect the braking and progressively wears out through the life of the brake pad. Once the brake pads have worn out, they are removed (with the brake disc and brake caliper in situ) by withdrawing the pads in a radially outward direction with respect to the brake disc. Various retaining features, such as pad springs and pad retainers, need to be removed before the worn brake pads can be removed.

[0004] Additionally, the brake caliper will include a housing on one side of the brake disc in which one or more pistons is mounted. A bridge is fixed to the housing (or is integral therewith) and straddles the brake disc to support a further brake pad on the opposite side of the brake disc. The housing and bridge together are known as a brake caliper frame.

[0005] The brake caliper frame is slidably mounted on a brake carrier, which in turn is non-rotatably mounted on suspension components adjacent to the brake disc.

[0006] During servicing of the caliper, the old worn brake pads are removed from the caliper in a radially outward direction. Clearly, the pads must be prevented from escaping from the caliper when the vehicle is in use. One known way of retaining the pads is to provide a pad retaining strap and bolt (as shown in FIG. 2).

[0007] UK patent application GB2303891, for example, shows a brake piston capable of applying a force to a brake pad to apply a brake. However, in this prior art structure the piston is a loosely fitted in a recess of the backplate of the brake pad. The piston is not attached to the brake pad. As such, this design will require additional features, such as a strap and/or bolt (not shown), to retain the pad in the caliper.

[0008] An object of the present invention is to provide an improved form of brake caliper that does not require complex pad retention structures.

SUMMARY OF THE INVENTION

[0009] One embodiment of the invention is directed to a brake caliper including a brake pad having a backplate with a friction material attached to one side and having a loading face on an opposite side, the caliper further including a piston for applying a force to the loading face in which the brake pad is releasably attached to the piston. By releasably securing the pad to the piston, it is not necessary to provide any other means of retaining the pad in the caliper.

[0010] The inventive alternative arrangement for pad retention, which uses features of the piston and brake pad, simplifies the process for retaining the pad in the caliper since a pad retaining strap and an associated bolt are no longer required. In particular, it is not necessary in the inventive structure to provide a pad strap retainer, a bolt or any associated machining.

[0011] According to a further aspect of the present invention, there is provided a kit of parts including a brake pad having a back plate with a friction material attached to one side and having a loading face on an opposite side, and a retaining means for releasably retaining the brake pad to a brake caliper piston or a brake caliper.

[0012] According to a further aspect of the present invention, there is provided a method of assembling a brake pad into a caliper comprising the steps of: providing a brake pad having a back plate with a friction material attached to one side and having a loading face on an opposite side, providing a caliper defining a brake disc plane and including a piston for applying a force to the loading face, inserting the brake pad into the brake caliper in a direction generally parallel to the brake disc plane, and moving one of the pad or piston in a direction generally perpendicular to the brake disc plane to simultaneously engage the piston with a location feature of the pad, thereby releasably attaching the pad to the piston.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0014]FIG. 1 is in isometric view of a known caliper assembly,

[0015]FIG. 2 is an exploded view of parts of the caliper assembly of FIG. 1,

[0016]FIG. 3 is an isometric view of a brake caliper according to the present invention,

[0017]FIG. 4 is a cross section view of the brake pad backplate of FIG. 3,

[0018]FIG. 5 is an enlarged cross section view of part of the piston and backplate of FIG. 3,

[0019]FIG. 6 is an alternative method of securing a piston and backplate of the present invention,

[0020] FIGS. 7 to 9 show a yet further method of securing a piston to a backplate of the present invention, and

[0021]FIG. 10 shows an exploded view of a piston/piston head subassembly according to a further aspect of the present invention.

[0022]FIG. 11 shows a schematic cross-section view of a caliper according to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023]FIGS. 1 and 2 show a known brake caliper 10 having a housing 12 and a bridge 14, which together form a frame 16. In this case, the housing 12 and bridge 14 are individual components that are bolted together, though the housing and bridge can be integrally formed as a single component. The frame is slidably mounted on a brake carrier 18, which is non-rotatably fixed to suspension components of an associated vehicle (not shown).

[0024] The frame 16 includes an aperture 20, which defines a disc brake plane. Mounted within aperture 20 are an inner brake pad 22 and an outer brake pad 24. The inner brake pad 22 is circumferentially positioned between two inner carrier abutments 26 (only one of which is shown in the Figures for clarity). The outer brake pad 24 is similarly positioned between two outer carrier abutments 28 (only one of which is shown in the Figures for clarity).

[0025] Two pistons 30 and 32 are mounted in the housing 12 and are actuated by an actuator (not shown) to force the inner brake pad 22 in the direction of arrow A of FIG. 2. This causes the inner brake pad 22 to move toward the brake disc. The reaction load of the actuator acts on the frame to cause the frame to move the outer brake pad 24 toward the brake disc, thus producing a braking torque on the disc. The brake pads 22 and 24 are identical and include a brake pad backplate 34 and friction material 36. In one structure, the backplate 34 is stamped from 8 mm thick sheet steel.

[0026] When the pistons are actuated to apply the brake, they each act through a piston head 38 and 40, which distribute the piston force across a larger area of the backplate 34. The piston heads 38 and 40 are retained on their respective pistons 30 and 32 by respective retaining rings 42 and 44. It should be noted that the piston heads are required because without them, the piston would apply very localized forces to small regions of the backplate, which in turn would cause uneven wear of the friction material due to flexing of the backplate during use.

[0027] Furthermore, it should be noted that the circumferential ends 46 and 48 of the backplate engage the inner carrier abutments 26 of the carrier 18 to transfer brake torque loads to the vehicle suspension. As the brake pads wear, the circumferential ends 46 and 48 move progressively towards the brake disc, progressively sliding along the inner carrier abutments 26. Clearly, the inner carrier abutment 26 is spaced from the outer carrier abutment 28 by a distance slightly greater than the thickness of the brake disc to allow the brake disc to sit therebetween. Thus, there is a gap between the edge of the brake disc and the edge of the inner carrier abutment, and a similar gap between the edge of the brake disc and the edge of the outer carrier abutment. As the brake disc wears, this gap increases and the thickness of the backplate 34 must be sufficient to ensure sufficient engagement of the backplate with the inner or outer carrier abutment when the friction material is fully worn and the brake disc has worn to its working limit.

[0028] Once the brake pads are worn, the retaining bolt 50 is unscrewed, allowing removal of the pad retainer 52. The worn pads 22 and 24 can then be withdrawn through the aperture 20 in the direction of arrow B of FIG. 1 (i.e. generally upwardly when viewing the Figure) clear together with the pad springs 54.

[0029] The pistons can then be wound back into the housing and the frame can be repositioned relative to the brake disc so that new pads can be inserted and secured in place with the pad retainer and bolt. It would be appreciated that the pads are withdrawn generally radially outwardly and are replaced by inserting them into the aperture in a generally radially inwardly direction.

[0030] The pad springs 54 provide for a limited amount of movement of the brake pad in a plane parallel to the disc brake plane. In particular, one of the functions of the pad spring is to reduce noise caused by rattling of the brake pad.

[0031] The friction material can be glued to the backplate, though under certain circumstances a more positive form of location is required to ensure sufficient shear strength at the backplate/friction material joint. Typically, the brake backplate may have holes drilled or stamped in it or a separate steel mesh may be welded to the friction material side of the backplate to receive friction material and hence increase the shear strength.

[0032] As noted above, the retaining bolt 50 and pad retainer 52 make removal and replacement of worn brake pads inconvenient. Further, the bolt 50 and retainer 52 are additional structures that increase the complexity of the braking system. The inventive structure eliminates a separate pad retention structure by using the pistons themselves as the pad retention structure.

[0033] More particularly, FIGS. 3 and 4 show one embodiment of the invention having a brake pad 59 with a brake pad backplate 60 that is generally planar. The brake pad 59 has a frictional material surface 62 on one side and a loading face 64 on an opposite side. The loading face includes two local load spreading features in the form of identical raised bosses 66 and 68. It should be noted that the top of the boss (when viewing FIG. 4) has a diameter d′, which is smaller than the diameter D of the lower portion of the boss. Thus the boss is able to act as a load spreading feature.

[0034] The boss 66, 68 is circular and has an edge 70 that tapers towards the loading face 64. The boss 66, 68 further includes a location feature in the form of a raised abutment 72. The abutment 72 is annular and has a diameter d′ that is slightly larger than the diameter d of the end 74A of piston 74.

[0035] The pistons 74 and 75 are both of substantially uniform circular cross section having diameter d. The following description will focus on one of the two pistons, but the description is applicable to both pistons. The end 74A (also known as a piston feature) of the piston 74 includes an annular groove 74B. A resilient means in the form of a wavy spring 76 is assembled into the groove 74B. The piston and spring are then inserted into the recess 73 formed by the surface 66A of the boss 66 and the raised abutment 72. This assembly process can either be achieved by moving the pad towards the piston or alternatively by moving the piston towards the pad as will be further described below.

[0036] The spring 76 is designed as an interference press fit in the recess 73, and hence the spring ensures that end 74A of the piston remains in contact with surface 66A when the associated vehicle is in use. In this way, the brake pad is positively attached to the piston in a releasable manner. The interference press fit ensures that the brake pad cannot inadvertently fall out or bounce out of the caliper during use, even if there is excessive pad-to-rotor clearance. Excessive clearance might occur if an associated brake adjuster fails to adjust the brakes following wear or if a partially failed wheel bearing results in excessive wobble of the brake disc, thereby knocking back the pad and piston into the caliper excessively. In particular, the inventive structure eliminates the need for a separate pad retainer. It will be appreciated that it is possible to design a caliper where the attachment between the brake pad and the piston is the sole means of preventing the brake pad inadvertently falling out or bouncing out of the caliper during use.

[0037] In addition to providing an interference push fit, the wavy spring also allows a limited amount of radial movement of the brake pad relative to the piston. In particular, the resilience of the wavy spring can be used to prevent pad rattle. Thus, in some applications, the wavy springs 76 and 77 fulfill the function of the pad spring 54 of the prior art.

[0038] Note that the wavy spring 76 is similar to proprietary components known as “tolerance rings”. Thus, under certain circumstances, it would be possible to design the piston and brake pad backplate to incorporate “off the shelf” tolerance rings rather than having a specific unique wavy spring.

[0039] The backplate 60 is generally arcuate and has circumferential ends 78 and 80. The circumferential ends 78 and 80 are locally thickened (T) when compared with the thickness (t) of the main portion of the backplate. This local thickening ensures that there is adequate engagement of the circumferential end with its associated carrier abutment even at the extremes of pad and disc wear. Similar local thickening (not shown) may be provided on a radially inner edge 82 of the backplate 60, where it abuts the associated caliper.

[0040] If necessary, one or more holes can be provided to receive friction material. Alternatively, or additionally the friction material surface 62 of the backplate 60 can be provided with recesses, in particular in the form of mesh, to improve the shear strength of the friction material/backplate joint.

[0041] In view of the above various features mentioned in relation to a brake pad backplate according to the present invention, it can be seen that there are several additional features when compared to known brake pad backplates stamped from sheet steel. Thus, while it is possible to machine various features from a solid backplate, or alternatively fabricate the components, it is particularly advantageous to provide some or all of these features integrally with a cast backplate, preferably cast from iron or steel.

[0042] The inventive brake pad backplate 60 has been described in with respect to a piston of an associated caliper 58 (see FIG. 11). Such a caliper can be generally similar to a known caliper 10 and would be designed to accommodate two identical brake pads according to the present invention. In particular, where the outer brake pad (i.e. the brake pad on the opposite side of the brake rotor to the piston) rests against the inner surface 91 of the caliper bridge, the caliper bridge can include formations which allow the brake pad to be releasably attached to the caliper. Thus, the inner surface of the bridge might typically include two annular projections 92 (only one shown on FIG. 11 for clarity), each projection having a diameter equivalent to the diameters of the pistons 75 and 74, and being spaced apart by a distance equivalent to the spacing of the pistons 75 and 74. Thus, it can be seen that these projections (also known as dummy piston features) are mirror images of the shape of the ends of pistons 74 and 75.

[0043] It should be noted that to remove the inner and outer brake pads 22 and 24 of the prior art shown in FIG. 2, for example during servicing, they are removed in a radial direction relative to the brake disc once the bolt and pad retainer have been removed.

[0044] However, the present invention provides a novel method of assembling brake pad backplates either during initial assembly or during re-assembly following servicing. Thus, in order to assemble the brake pad backplate 60 in the outer position of the caliper (i.e., into the position equivalent to pad 24 of FIG. 1), the pad has to be inserted in a radial direction and then subsequently moved in an axial direction, away from the brake disc, to engage the location of features of the backplate with further features (e.g., the dummy piston features) on the inner face of the bridge, thereby simultaneously fitting the brake pad and attaching the brake pad to the dummy piston feature.

[0045] Similarly, when the backplate 60 is assembled in an inner position (i.e. in a position equivalent to the pad 22 of FIG. 1), the backplate 60 has to be first moved in a radially inward direction and then in an axial direction away from the brake disc so that the location features of the backplate engage with the pistons, thereby simultaneously fitting the brake pad and attaching the brake pad to the piston.

[0046] An alternative method of assembling the backplate 60 into a caliper is to first move the backplates in a radial direction so that the friction material is proximate the brake disc surface, and then to apply the brake so that the piston and the inner face of the bridge approach and engage with location features on the backplate, thereby preventing escape of the pads during subsequent normal use of the vehicle.

[0047] Thus, the inventive method of assembly of the present invention is to provide axial movement of the backplate relative to the piston or relative to the bridge as appropriate to engage the location feature and prevent the escape of the backplate from the caliper during subsequent normal use of the vehicle.

[0048]FIG. 6 shows an alternative piston structure 174 including a larger groove 174B designed to accommodate the retaining ring 42. This piston and retaining ring subassembly can be assembled onto the backplate 60 according to the present invention. In this case the retaining ring 42 is an interference fit with the recess 73 of the backplate 60.

[0049] FIGS. 7 to 9 show an alternative piston structure 274 having a groove 274B. An alternative brake pad backplate 260 is provided which, in this case, includes chordally-oriented holes 284. In this case, the piston 274 is inserted into the recess 273 and then the spring clip 286 is inserted in the direction of arrows A through the holes 284 such that regions 287 of the spring clip sit within the groove 274B, thus retaining the piston to the pad.

[0050] In further embodiments, a single pin could be used. Such a single pin could be radially or chordally-oriented relative to the piston. The pin could be arranged to fit in a hole of the piston, rather than in a circumferential groove of the piston.

[0051]FIG. 3 shows a piston feature (the piston end) in the form of a projection, which engages in a recess of the brake pad backplate. In further embodiments, a projection on the brake pad backplate could be arranged to engage a recess in the piston.

[0052] It will be appreciated that the wavy springs 76 and 77 act as retaining features to retain the pad to the piston. Similarly, the retaining ring 42 when used as shown in FIG. 6 acts as a retaining feature. Again, spring clip 286 acts as a retaining feature.

[0053] When a set of brake pads according to the present invention have been worn out through use, then a brake pad kit will be purchased in order to replace the worn brake pads. This kit might typically include a set of brake pads, along with appropriate retaining features, i.e. a set of wavy springs 76, or a set of retaining rings 42, or a set of spring clips 286.

[0054] The invention has been hereinbefore described in relation to a novel and inventive brake caliper. However, the wavy spring 76 described above can be used to attach a piston 74 to the known piston head 38 to form a piston/piston head sub-assembly 90 (see FIG. 10). This sub-assembly can be used in prior art calipers with prior art brake pad backplates 34. In particular, the wavy spring 76 provides an additional anti-rattle feature that can be incorporated in known brake assemblies.

[0055] In this case, the wavy spring is received in the groove 74B of the piston 74. In an alternative embodiment, the piston head 38 could be provided with an internal groove to receive wavy spring 76, and thus piston 74 would not require the groove 74B. It would be appreciated that, in a similar manner, the grooves of piston 74 and 75 as shown in FIG. 3 could be transferred to the corresponding recesses on the brake backplate 60.

[0056] It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby. 

1. A brake caliper comprising: a brake pad having a backplate with a friction material attached to one side and having a loading face on an opposite side; and a piston for applying a force to the loading face, wherein the brake pad is releasably attached to the piston.
 2. A brake caliper as defined in claim 1, wherein the brake pad comprises a location feature and the piston comprises a piston feature, wherein the location feature cooperates with a piston feature of the piston to locate the brake pad relative to the piston and to releasably attach the brake pad to the piston.
 3. A brake caliper as defined in claim 2, wherein the piston feature is one of a projection and recess and the location feature is the other of a projection and recess.
 4. A brake caliper as defined in claim 1, further comprising a resilient means disposed between the piston and the brake pad to releasably secure the brake pad to the piston.
 5. A brake caliper as defined in claim 4, wherein the resilient means permits limited movement of the brake pad in a plane of the brake pad relative to the piston.
 6. A brake caliper as defined in claim 4, wherein the piston feature is one of a projection and recess and the location feature is the other of a projection and recess and the resilient means is press fitted on at least one of the projection and the recess.
 7. A brake caliper as defined in claim 6, wherein the resilient means is press fitted on one of the projection and recess and is mounted in a groove of the other of the projection and recess.
 8. A brake caliper as defined in claim 4, wherein the resilient means is one selected from the group consisting of a spring and a tolerance ring.
 9. A brake caliper as defined in claim 1, wherein the brake pad is releasably attached to the piston by a pin engaging the brake pad and piston.
 10. A brake caliper as defined in claim 9, wherein the pin is disposed in an orientation selected from the group consisting of a radial orientation and a chordal orientation relative to the piston.
 11. A brake caliper as defined in claim 10, wherein the pin has a chordal orientation and engages a circumferential groove in the piston.
 12. A brake caliper as defined in claim 2, further comprising: a bridge defining a brake disc plane; a second brake pad having a back plate with a friction material attached to one side and having a loading face on an opposite side, wherein the second brake pad includes a second location feature substantially identical to the location feature; and a dummy piston feature substantially identical to the piston feature, wherein the second location feature cooperates with the dummy piston feature to locate the second brake pad relative to the caliper and to releasably attach the brake pad to the caliper.
 13. A brake caliper as defined in claim 12, wherein a resilient means acts between the caliper and the second brake pad to releasably attach the second brake pad to the caliper.
 14. A brake caliper as defined in claim 12, wherein the second brake pad is releasably attached to the caliper by a pin engaging the brake pad and the dummy piston feature
 15. A brake caliper as defined in claim 14, wherein the pin is disposed in an orientation selected from the group consisting of a radial orientation and a chordal orientation relative to the piston.
 16. A brake caliper as defined in claim 12, wherein the second brake pad is releasably attached to a second dummy piston feature.
 17. A brake caliper as defined in claim 1, further comprising a second piston, wherein the brake pad is releasably attached to the piston and the second piston.
 18. A kit of parts for a brake assembly, comprising: a brake pad having a back plate with a friction material attached to one side and having a loading face on an opposite side; and a retaining means for releasably attaching the brake pad to a brake caliper piston or a brake caliper.
 19. A kit of parts as defined in claim 18, wherein the retaining means is at least one selected from the group consisting of a resilient means and a pin.
 20. A method of assembling a brake pad into a caliper having a brake pad with a back plate with a friction material attached to one side and with a loading face on an opposite side, the caliper defining a brake disc plane and including a piston for applying a force to the loading face, the method comprising: inserting the brake pad into the brake caliper in a direction generally parallel to the brake disc plane; and moving at least one of the brake pad and the piston in a direction generally perpendicular to the brake disc plane to simultaneously engage the piston with a location feature of the pad, thereby releasably attaching the pad to the piston.
 21. A piston/piston head subassembly, comprising: a piston; a piston head; and a resilient means that secures the piston to the piston head, the spring allowing a limited amount of movement of the piston head in a plane perpendicular to a piston axis. 